Electrical connector

ABSTRACT

A device for forming an electrical connection between part of an elongate electrical conductor between its ends and one or more other electrical conductors comprises and electrically insulating sleeve, a metallic connecting element located within the sleeve, and a quantity of solder for forming a permanent electrical connection between the conductors. The electrically insulating sleeve and the connecting element have two open ends to allow the elongate electrical conductor to extend through them, and the connecting element has a tapering internal surface which has a screw thread to enable the other electrical conductor or conductors to be held in contact with the elongate electrical conductor by twisting the connecting element about the conductors.

This invention relates to electrical connectors, and especially toconnectors for forming solder joints between conductors in such articlesas automotive harnesses and the like.

Electrical harnesses, for example as manufactured in the automotiveindustry, are often quite complex. In some instances they aremanufactured by forming two or more sub-assemblies of wires, terminals,connectors and any other components, and then forming electricalconnection(s) between the sub-assemblies. In such a case the assembly ofthe harness may be controlled by computer permitting, with the aid of amonitor, the assembly operator to see schematically the lay up and tocheck correct build-up of the assembly at each stage of the harnessmanufacture. In order to enable this control process to operate the endsof the conductors of the sub-assemblies are connected, e.g. by means ofspring contacts, and an electrical current or signal is passed throughthe assembly in order to obtain verification that the harness iscorrect. It is only after such verification is obtained that the clipsare removed and a permanent electrical connection is formed.

A device for forming temporary and a permanent electrical connectionthat is suitable in such a circumstance is described in our co-pendinginternational application No. PCT/GB91/01016, the disclosure of which isincorporated herein by reference. According to the present inventionsuch a device is modified in order to enable electrical conductors to beconnected to an intermediate part of an elongate conductor. Thus,according to one aspect, the present invention provides a device forforming an electrical connection between part of an elongate electricalconductor between its ends and one or more other electrical conductors,which comprises an electrically insulating sleeve, a metallic connectingelement located within the sleeve, and a quantity of solder for forminga permanent electrical connection between the conductors, theelectrically insulating sleeve and the connecting element having twoopen ends to allow the elongate electrical conductor to extendtherethrough, and the connecting element having a tapering internalsurface which has a screw thread to enable the other electricalconductor or conductors to be held in contact with the elongateelectrical conductor by twisting the connection element about theconductors.

The device according to the invention may be employed to form anelectrical connection in a very quick and simple manner. Thus, accordingto another aspect, the invention provides a method of forming aconnection between part of an elongate electrical conductor between itsends and one or more other electrical conductors, which comprises:

(i) sliding a device comprising an electrically insulating sleeve and ametallic connecting element located within the sleeve along the elongateelectrical conductor, the insulating sleeve and the connecting elementhaving open ends to allow the elongate electrical conductor to extendtherethrough and the connecting element having a tapering internalsurface which has a screw thread;

(ii) inserting one or more other electrical conductors into one end ofthe sleeve and connecting element;

(iii) twisting the device about the conductors so that the connectingelement holds the other conductor or conductors in contact with theelongate electrical conductor; and

(iv) heating the device in order to form a solder connection between theconductors.

The device according to the invention has the advantage that theconductors can be electrically joined to form a temporary joint which isdisconnectable but is able to have a high degree of dependability, inorder, for example to test the connected conductors, and can then bepermanently joined with no further manipulation of the joint but simplyby heating the sleeve in order to melt the solder. In addition, thetapering interior of the connecting element enables bundles formed froma range of conductor sizes to be handled by the device.

In the broadest aspect of the invention the device includes a connectingelement having a single tapering internal surface so that a connectioncan be formed with conductors having a range of sizes. However, it ispossible for devices according to the invention to include connectingelements having more than one tapering internal surface. Thus, theconnecting element may have an internal surface that tapers from eachend thereof toward a central part of smaller diameter in order to allowone or more other electrical conductors to be inserted from each endthereof. In such a case the connecting element may be formed from a pairof parts that can be rotated with respect to each other, or it may beformed with the threads in the tapering internal surfaces being ofopposite senses to each other so that conductors inserted into both endsof the connecting element can be secured by rotating the element in onedirection.

The invention may be employed to form a connection to a single conductorwire, ie. an unscreened wire, but more usually it will be employed toform a connection to a central part of a screen, for example of acoaxial cable, screened twisted pair or the like. In such a case anyinsulation over the screen at the point of connection is removed toexpose the screen, and the device is slid along the cable until theconnecting element thereof is positioned over the exposed screen. In thecase of a connecting element formed by coiling a wire, it is possible ifthe size of the device is matched correctly to that of the cable, forthe insulated cable to force the smallest diameter winding of theconnecting element to open slightly to a larger diameter. When thedevice has been slid along the cable to the exposed part of the screenthe last winding of the connecting element will relax to its originalsize and grip the screen.

Usually the sleeve will be dimensionally recoverable, and especiallydimensionally heat-recoverable, that is to say the article has adimensional configuration that may be made substantially to change whensubjected to heat treatment.

Usually these articles recover, on heating, towards an original shapefrom which they have previously been deformed but the term"heat-recoverable", as used herein, also includes an article which, onheating, adopts a new configuration, even if it has not been previouslydeformed.

In their most common form, such articles comprise a heat-shrinkablesleeve made from a polymeric material exhibiting the property of elasticor plastic memory as described, for example, in U.S. Pat. Nos.2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example,U.S. Pat. No. 2,027,962, the original dimensionally heat-stable form maybe a transient form in a continuous process in which, for example, anextruded tube is expanded, whilst hot, to a dimensionally heat-unstableform but, in other applications, a preformed dimensionally heat-stablearticle is deformed to a dimensionally heat unstable form in a separatestate.

In the production of heat-recoverable articles, the polymeric materialmay be cross-linked at any stage in the production of the article thatwill enhance the desired dimensional recoverability. One manner ofproducing a heat-recoverable article comprises shaping the polymericmaterial into the desired heat-stable form, subsequently cross-linkingthe polymeric material, heating the article to a temperature above thecrystalline melting point or, for amorphous materials the softeningpoint, as the case may be, of the polymer, deforming the article andcooling the article whilst in the deformed state so that the deformedstate of the article is retained. In use, since the deformed state ofthe article is heat-unstable, application of heat will cause the articleto assume its original heat-stable shape.

Any material to which the property of dimensional recoverability may beimparted may be used to form the sleeve. Preferred materials includelow, medium or high density polyethylene, ethylene copolymers, e.g. withalpha olefins such as 1-butene or 1-hexene, or vinyl acetate, polyamidesor fluoropolymers, e.g. polytetrafluoroethylene, vinylidine fluoride orethylenetetrafluoroethylene copolymer.

The fact that the ends of the conductors are enclosed in the connectionelement will also reduce the risk of any strands of the conductorspiercing the sleeve during recovery thereof. Also, the conductingelement can act as a heat-sink thereby preventing overheating of thedevice during recovery.

At least in the broadest aspect of the invention the connecting elementmay generally have any form although it is preferred for it to be formedby coiling a piece of wire into a tapering coil so that the windingsform the screw thread. Preferably the internal surface of the connectingelement is at least partly conical, for example it may be conical orfrusto-conical. If the connecting element is formed from a wire, it cangrip the bundle of conductors introduced therein due to the resilienceof the wire and the fact that it will be enlarged radially to someextent by the introduction of the bundle. However, in one advantageousform of device it has been radially expanded from its relaxed stateduring manufacture of the device and to be retained in its expandedstate so that it will radially contract, or attempt radially tocontract, when the permanent connection is formed. Thus, for example,the spring may be held out against its resilient recovery forces by thesleeve or by the solder, so that softening of the sleeve or melting ofthe solder will allow the spring to recover. For example, a boss may beformed on the internal surface of the sleeve or on the internal surfaceof the solder which will disappear when the device is heated. The degreeof expansion need not be great, for example it may be not more than 5%or even not more than 2%, since it may be desirable that the coilremains in contact with the solder element when the device is heated.

The wire may be formed with a circular cross-section, although it ispreferred for the wire to have a relatively sharp ridge along itslength, e.g. formed by cold drawing or cold rolling, which, when thewire has been coiled, is directed toward the interior of the coil inorder to form the screw thread. In particular it is advantageous for thewire to be formed with a polygonal cross-section and especially a squareor rhombic cross-section. The wire may be formed from any appropriatemetal or metal alloy, but preferably is formed from copper, andespecially from copper having substantially the same purity as thatconventionally employed for electrical conductors.

As mentioned above, the device includes a quantity of solder, ie. aquantity of soft solder as distinct from brazing material, for forming apermanent solder connection. The solder may, for example, simply be inthe form of an Sn₆₃ Pb₃₇ eutectic composition which will melt as thedevice is heated and the sleeve recovers, or more than one soldercomposition having differing melting points may be employed, asdescribed in International Application No. WO88/09068. In this form ofdevice, melting of the higher melting point component, e.g. Sn₉₆.5 Ag₃.5eutectic will provide a visual indication that the device has beenheated sufficiently to melt the lower melting point composition and toform a satisfactory solder joint. If desired the lower melting pointsolder may be a non-eutectic composition and, for example as describedin International Application No. PCT/GB90/00234, the higher and lowermelting point solder compositions may together form a eutecticcomposition. For example, a non-eutectic Sn₆₀ Pb₄₀ lower melting pointcomponent may be employed with a higher melting point component formedfrom pure tin in relative amounts that an Sn₆₃ Pb₃₇ eutectic is formed.The disclosures of these two patent applications are incorporated hereinby reference. An advantage of employing a two component solder, andespecially a tin, Sn₆₀ Pb₄₀ combination is that it reduces thepossibility of "wicking" that is to say, travel of the solder along theconductors and away from the joint area due to capillary action by thestranded conductors, which can be caused by prolonged heating of thedevice.

The solder may be positioned anywhere where it will be able to flow intothe connecting element to form a solder joint. The solder may beemployed in the form of a ring or in any other form for example a ball,and may be disposed symmetrically about the sleeve axis or offset fromit. The solder element may, for instance, be located at the smallerdiameter end of the connecting element in which case it may be in theform of a ball or plug, or it may be located in the region of a largediameter end of the connecting element, for example in the form of aring. Preferably the solder is in the from of an element that surroundsthe connecting element, especially where the connecting element is inthe form of a coil so that the fused solder can flow through thewindings of the coil to the interior thereof. More than one quantity ofsolder may be employed, for example where the connecting element hasmore than one tapering internal surface for forming a splice.

Although it is not essential, the sleeve will normally be provided withone or more sealant inserts in order to reduce or prevent ingress ofmoisture into the connection. For example the sleeve may contain aninsert, e.g. in the form of a ring, of a fusible polymeric materialwhich will melt when the device is heated to melt the solder. Materialsthat may be used to form the fusible insert include alkylene homo- andcopolymers, e.g. polyethylene or ethylene-vinyl acetate copolymer,polyamides e.g. those based on dimer diamines, and polyesters.

Several devices in accordance with the present invention will now bedescribed by way of example with reference to the accompanying drawingsin which:

FIG. 1 is a section through one form of device according to theinvention;

FIG. 2 is a section through the device during installation on a coaxialcable;

FIG. 3 is a section through the device at a later stage duringinstallation;

FIG. 4 is a section through the device after completion of theconnection; and

FIG. 5 is a section through a second form of device according to theinvention during installation.

Referring initially to FIGS. 1 to 4, a device 1 for forming anelectrical connection between the braid of a screened cable 2 comprisesa dimensionally heat-recoverable sleeve 3 having two open ends 4 and 5.The sleeve contains a connecting element 6 that has been formed from ahard tempered copper wire by coiling it to form a tapering helix. Thewire has a cross-section in the form of a sector of a circle and it isoriented so that the circular side of the wire forms the exteriorsurface of the connecting element. A strip of solder 7 is located aroundthe connecting element and pressed onto it to form the solder into afrusto-conical shape that accommodates itself to the outer surface ofthe connecting element.

The sleeve 3 is formed from cross-linked polyvinylidine fluoride andcontains a pair of fusible rings 8 and 9, the rings being located atopposite ends of the connecting element 6. The rings 8 and 9 are formedfrom uncrosslinked polyethylene or may be formed from another plasticsmaterial that will produce a good seal to an specific cable jacket.

In order to form an electrical connection to the braid of a shieldedcable 2 a portion of the jacket is removed by centre stripping to exposethe braid 10. The device 1 is then slipped over one end of the cable andslid toward the exposed portion of braid 10 as shown in FIG. 2. The sizeof the device 1 should be chosen so that the smaller diameter end of theconnecting element 6 is very slightly smaller than the diameter of thebraid so that the smaller diameter end of the connecting element isforced to enlarge as it is pushed over the cable jacket. When the deviceis located over the exposed braid 10 the connecting element 6 willreturn to its original shape and the smaller diameter end will grip thebraid. A number of insulated wires 11 whose ends have been stripped ofinsulation are then inserted into the open end 4 of the sleeve 3 untiltheir stripped ends are positioned within the connecting element asshown in FIG. 3. The device 1 is then twisted about the cable 2 andwires 11 so that the screw thread formed by the wire of the connectingelement bites into the exposed conductors of the wires 11 and firmlygrips the conductors. The electrical performance of the harness formedfrom the cable 2 and wires 11 can then be tested and afterwards thedevice 1 can be heated for example by means of a hot-air gun or aninfrared lamp to cause the solder 7 to flow and form a permanent solderconnection between the braid 10 and the wires 11. When the device 1 isheated the fusible rings 8 and 9 will also melt and flow to seal thedevice against ingress of water into either end thereof.

FIG. 5 shows a second form of device in which the connecting element 6has two frusto-conical halves which are joined at their smaller diameterends to form a single element having a narrow waist. In this case theelement is formed from a single piece of wire although it is possible toform the element 6 so that one half is rotatable with respect to theother. As shown wires 11 can be inserted into both ends of theconnecting element 6 and can be gripped by rotating the device 1 aboutthe cable and wires. The wire, forming the connecting element 6 is woundin opposite senses in different halves of the element so that rotationof the device about the cable 2 and wires 11 will cause the wires inboth halves of the element to be gripped.

I claim:
 1. A device for forming an electrical connection between partof an elongate electrical conductor between its ends and one or moreother electrical conductors, which comprises an electrically insulatingsleeve, a metallic connecting element located within the sleeve, and aquantity of solder for forming a permanent electrical connection betweenthe conductors, the electrically insulating sleeve and the connectingelement having two open ends to allow an elongate electrical conductorto extend therethrough, and the connecting element having a taperinginternal surface which has a screw thread to enable the other electricalconductor or conductors to be held in contact with the elongateelectrical conductor by twisting the connection element about theconductors.
 2. A device as claimed in claim 1, wherein the sleeve isdimensionally heat-recoverable.
 3. A device as claimed in claim 1,wherein the connecting element is formed by coiling a piece of wire intoa tapering coil.
 4. A device as claimed in claim 3, wherein the coil hasbeen radially expanded from its relaxed state and is retained in itsexpanded state so that it will radially contract, or attempt radially tocontract when the permanent connection is formed.
 5. A device as claimedin claim 3, wherein the wire has a relatively sharp ridge along itslength which is directed toward the interior of the coil in order toform the screw thread.
 6. A device as claimed in claim 3, wherein thewire has a polygonal cross-section.
 7. A device as claimed in claim 1,wherein the connecting element is formed from copper.
 8. A device asclaimed in claim 1, wherein the solder is formed from a plurality ofcompositions that have differing melting points.
 9. A device as claimedin claim 1, wherein the solder is in the form of an element, is locatedaround the connecting element.
 10. A device as claimed in claim 9,wherein the solder element is frusto-conical in shape and sits incontact with the connecting element.
 11. A device as claimed in claim 9,wherein the connecting element has an internal surface that tapers fromeach end thereof toward a central part of smaller diameter in order toallow one or more other electrical conductors to be inserted from eachend thereof.
 12. A device as claimed in claim 1, wherein the sleevecontains one or more inserts of a fusible polymeric material in order toform a seal against ingress of moisture.
 13. A method of forming aconnection between part of an elongate electrical conductor between itsends and one or more other electrical conductors, which comprises:(i)sliding a device comprising an electrically insulating sleeve and ametallic connecting element located within the sleeve along the elongateelectrical conductor, the insulating sleeve and the connecting elementhaving open ends to allow the elongate electrical conductor to extendtherethrough and the connecting element having a tapering internalsurface which has a screw thread; (ii) inserting one or more otherelectrical conductors into one end of the sleeve and connecting element;(iii) twisting the device about the conductors so that the connectingelement holds the other conductor or conductors in contact with theelongate electrical conductor; and (iv) heating the device in order toform a solder connection between the conductors.